1. Field of the Invention
The present invention relates, in general, to an apparatus and method for measuring the thickness and profile of a transparent thin film and, more particularly, to an apparatus and method for measuring the thickness and profile of a transparent thin film using a white-light interferometer.
2. Description of the Related Art
FIG. 1 is a diagram showing the construction of an apparatus for measuring the thickness and profile of a transparent thin film using a conventional white-light interferometer.
The apparatus of FIG. 1 has a structure in which a Michelson interferometer module having a blocking surface is combined with an acousto-optic tunable filter capable of scanning a visible spectrum region. Such a structure can independently measure the thickness and profile of a thin film by turning on or off the blocking surface.
The apparatus of FIG. 1 applies an Acousto-Optic Tunable Filter (hereinafter referred to as “AOTF”) 40 to a white-light interference system, so that thickness information and profile information can be separated and independently measured using the interference of monochromatic light with respect to a multi-layered measurement unit 80 composed of a fine thin film layer 83 applied to an opaque metallic layer pattern 82.
A light source 10 for emitting white light is connected to one end of an optical fiber 11 and emits the white light to the other end of the optical fiber 11. The white light, having passed through the optical fiber 11, passes through a fixing member 12 having a central pinhole and spreads from the pinhole. The white light is aligned to have a certain width while passing through a first convex lens 13, and the aligned white light is then incident on a first beam splitter 20. White light passing through the first beam splitter 20 is radiated onto a second convex lens 31. Part of the white light is reflected toward a reference surface 33 while white light passes through the second convex lens 31 and the second beam splitter 32, and the remaining part of the white light penetrates through the second convex lens 31 and the second beam splitter 32 and is radiated onto a measurement unit 80.
A blocking plate 34 is located in front of the reference surface 33 while being spaced apart from the reference surface 33 by a predetermined distance. The blocking plate 34 is parallel to the reference surface 33 at a location close to the reference surface 33, and selectively blocks white light incident on the reference surface 33.
A system including the second convex lens 31, the second beam splitter 32 and the reference surface 33 is a Michelson interferometer module 30. The blocking plate 34 is included in the Michelson interferometer module, so that the Michelson interferometer module 30 is operated in two modes depending on the selective blocking of white light by the blocking plate 34. Further, the white light, which is split by the second beam splitter 32 and is incident on the reference surface 33 and the measurement unit 80, causes variation in wavelength while being radiated onto the measurement unit 80. Such variation is caused because the measurement unit 80 has profile information and thickness information. The profile information and the thickness information can be separated and measured in respective modes based on the operation of the blocking plate 34. The radiated white light is reflected and incident on the AOTF 40. The AOTF 40 performs a filtering operation to separate white light in a frequency band that has thickness information or profile information from white light in the remaining frequency band. The white light, output from the AOTF 40, is focused onto a Charge Coupled Device (CCD) sensor 70 after passing through a third convex lens 50, thus forming an image. The white light focused onto the CCD sensor 70 is scanned as a spectral image to extract respective pieces of information from the spectral image. Further, information about the profile of the fine thin film layer 83 of the measurement unit 80 can be finally obtained using peak point information obtained from the extracted information.
However, such an interferometer is disadvantageous in that, since the filtering range and resolution of an AOTF greatly influence the performance of a system, and a short wavelength of a specific band is selectively scanned, the interferometer performs poorly with respect to real-time measurement and external vibrations. Further, in order to independently obtain the thickness and profile of a thin film, a blocking surface must be turned on or off using hardware, so there is difficulty in simultaneously obtaining two pieces of information. Further, there is a disadvantage in that, since a plurality of unknown quantities related to the thickness and profile of a thin film is obtained using a least square fitting method based on numerical analysis, the time required for measurement greatly increases.